One of the most important questions they had to consider was of public healthA. whatB. thi

问题补充：

One of the most important questions they had to consider was of public health

A. what

B. this

C. that

D. which

答案：

A. what

B. this

(答案→)C. that

D. which

解析：句意为：他们必须考虑其中最重要的问题是公共卫生。考查that作代词，that 作代词，往往用于特指，相当于“that＋名词”，它也只能代替事情不能代替人。